Synchronous generators are frequently used to generate electric power. When such machines are designed as internal rotors, they have an external winding (stator winding) that generates a magnetic rotational field. A magnet wheel (rotor) carries either permanent magnets or an energizer winding to generate the field. With these polyphase machines, the rotor rpm is equal to the number of rotating fields. The stator is comprised of stratified magnetic iron plates insulated electrically from one another and is designed to reduce eddy current losses. The stator winding is inserted and wired into axially parallel grooves between the poles of the stator pointing radially inward. The alternating magnetic fields revolving with the movement of the rotor overcome the air gap between the rotor poles and stator poles and intersect with the stator windings. An alternating voltage is generated in each of the windings because of the magnetic fields which alternate with each revolution of the rotor, the frequency of this alternating voltage being synchronous with the rotor rpm. Through a suitable arrangement and wiring of stator windings, the synchronous machine may generate single-phase or polyphase alternating voltage. In generator operation, the active power is determined by the angular displacement, which is obtained as the angle of rotation between the rotor of the loaded machine and the off-load machine. If the angle of rotation becomes too large, the machine rpm increases drastically and the machine may be destroyed due to the centrifugal force acting on its own components. In this operating state, it must be shut down as quickly as possible and resynchronized. For use in the aviation sector in particular, electric/mechanical access to the generator is impossible for obvious reasons. Furthermore, the electromechanical efficiency of synchronous machines is limited not least of all because of the winding overhangs.
Machines related to permanent-field synchronous machines in terms of their basic design include transverse flux machines which have a hoop winding, in contrast with normal machines having full-pitch windings. The magnetic flux runs transversely (perpendicularly) to the plane of rotation. A rotor has multiple permanent magnet rings arranged adjacent to one another axially, each ring comprised of individual magnets oriented radially with alternating magnetic directions. The stator has one or more hoop windings which are encircled by intermeshing soft magnetic poles. When the rotor moves in relation to the stator, an alternating magnetic flux is passed through each stator coil, inducing a generator voltage.
Decoupling of the magnetic and electric circuits in transverse flux machines facilitates their respective dimensioning. In addition, this eliminates the so-called winding overhangs which are customary with synchronous machines and do not contribute to generation of torque. Machines that operate according to the transverse flux principle may thus have considerably lower ohmic losses due to the design than a longitudinal flux motor that is otherwise comparable in terms of the magnetic shear forces. This permits a much finer pole pitch, which already results in a high torque and a higher efficiency at a low rpm. However, transverse flux machines have a more complex mechanical design. High efficiencies can be achieved with permanent-field machines, but the permanent magnets to be used with them are cost-intensive.
The disadvantages of both synchronous machines and the traditional transverse flux machines as mentioned above may still be acceptable in some applications but they are unacceptable in the aviation sector due to the high safety demands. Aircraft engines are subject to constantly increasing demands. The important thing in this field is to discover any error incidents and error sequences that do occur as soon as possible; the possibilities for avoiding these errors are important. An error-tolerant design of the propulsion unit and its components contributes to such safety if it does not lead to any major consequences in a fault incident.
Therefore, the object of the present invention is to provide a transverse flux machine which has a high inherent operating reliability and in which any fault incident that nevertheless occurs can be brought to a safe state (fail-safe).